The leading causes of death in the U.S. are cardiovascular diseases and cancer. Both types of diseases are thought to be partially the result of oxidative stress, which can lead to damage of biomolecules. It has been hypothesized that an increase in dietary antioxidants can reduce oxidative stress and prevent chronic diseases. Doll and Peto (J. Natl. Cancer Inst. 66:1192-1308 (1981)), estimated that 35% (range 10-70%) of deaths from cancer could be avoided by dietary modifications. Willett (Environ. Health Perspect. 103:165-170 (1995)) later narrowed the range to 20-42%, stating that roughly 32% of cancers could be prevented by changes in diet. Fruits and vegetables contain many compounds, including phenolics, thiols, carotenoids, tocopherols, and glucosinolates, that may exert chemoprotective effects through a variety of mechanisms (Dragsted et al., Pharmacol. Toxicol. 72:116-135 (1993)). Increased intake of fruits and vegetables has also been associated with reduced risk of coronary heart disease (CHD) (Joshipura et al., Ann. Intern. Med. 134:1106-1114 (2001)) and stroke (Gillman et al., J. Am. Med. Assoc. 273:1113-1117 (1995)). Flavonoids, commonly found in fruits and vegetables, have been linked to reduced risk or mortality from CHD (Hertog et al., Lancet 342:1007-1011 (1993)). Such findings have lead the National Research Council (NRC) to recommend consuming five or more servings of fruits and vegetables a day.
Apples are a very significant part of the diet. From a Dutch Food Consumption Survey and previously analyzed flavonoid contents of fruits, vegetables, and beverages, Hertog et al. (Nutr. Cancer 20:21-29 (1993)) determined that apples are the third largest contributors of flavonoids in the Dutch diet behind tea and onions. In Finland, along with onions, apples are the top contributors (Knekt et al., Am. J. Epidemiol. 146:223-230 (1997)). Twenty-two percent of the fruit phenolics consumed in the U.S. are from apples, making them the largest source (Vinson et al., J. Agric. Food Chem. 49:5315-5321 (2001)). Consumption of apples has been linked to the prevention of chronic disease. Apple intake has been negatively associated with lung cancer incidence in two separate studies (Knekt et al., Am. J. Epidemiol. 146:223-230 (1997); Le Marchand et al., J. Natl. Cancer Inst. 92:154-160 (2000)). It has also been related to reduced cardiovascular disease. Coronary and total mortality (Knekt et al., Brit. Med. J. 312:478-481 (1996)), symptoms of chronic obstructive pulmonary disease (Tabak et al., Am. J. Respir. Crit. Care Med. 164:61-64 (2001)), and risk of thrombotic stroke (Knekt et al., Eur. J. Clin. Nutr. 54:415-417 (2000)) have all been inversely associated with apple consumption.
Apples are a good source of phenolic compounds (Eberhardt et al., Nature 405:903-904 (2000)). The total extractable phenolic content has been investigated and ranges from 110-357 mg/100 g fresh apple (Podsedek et al., Eur. Food Res. Technol. 210:268-272 (2000); Liu et al., N.Y. Fruit Q. 9:15-17 (2001)). It is known that the concentration of total phenolic compounds is much greater in the peel of apples than in the flesh (Burda et al., J. Agric. Food Chem. 38:945-948 (1990); Ju et al., Postharvest Biol. Technol. 8:83-93 (1996); Escarpa et al., J. Chromatogr. 823:331-337 (1998)). The nature and distribution of these phytochemicals between the flesh and the peel of the apple is also different. For example, while the fleshy part of the apple contains catechins, procyanidins, phloridzin, phloretin glycosides, caffeic acid and chlorogenic acid, the apple peel possesses all of these compounds and has additional flavonoids not found in the flesh, such as quercetin glycosides and cyanidin glycosides (Burda et al., J. Agric. Food Chem. 38:945-948 (1990); Escarpa et al., J. Chromatogr. 823:331-337 (1998); Golding et al., J. Agri. Food Chem. 49:2283-2289 (2001); van der Sluis et al., J. Agri. Food Chem. 49:3606-3613 (2001)). It has been noted in other fruits and vegetables that the peels have high phytochemical concentrations and/or high antioxidant activity (Talcott et al., J. Agric. Food Chem. 48:4590-4596 (2000); Gil et al., J. Agric. Food Chem. 48:4581-4589 (2000); Talcott et al., J. Agric. Food Chem. 48:1315-1321 (2000); Ewald et al., Food Chem. 64:231-235 (1999); Mizuno et al., Nippon Shokuhin Kogyo Gakkaishi 39:88-92 (1992); Hirota et al., J. Agric. Food Chem. 46:3497-3502 (1998)).
Peeled and unpeeled apples have high antioxidant activity and inhibit the growth of human cancer cells in vitro (Eberhardt et al., Nature 405:903-904 (2000)). The antioxidant and antiproliferative activities of unpeeled apples is greater than that of peeled apples (Eberhardt et al., Nature 405:903-904 (2000)). Apple peels are a waste product of applesauce and canned apple manufacture. Industrially, apples are peeled both by using a hot caustic method and mechanically. The National Agriculture Statistics Service (NASS) (USDA, National Agriculture Statistics Service, 2002) reported that 267 million pounds of apples were processed in applesauce and canned apple production in New York State alone in 2001. The apple peels are typically used for non-valuable purposes. For instance, the peels, along with the core materials of the apples, are often pressed to make juice or vinegar, pressed into a cake for livestock feed, or used as fertilizer. Sometimes apple peels and core materials are used as a source of pectin.
An attempt was made in the past to create a valuable product from apple peels (Bomben et al., Food Technol. 25:1108-1117 (1971)). The peels from apples were soaked, macerated and mixed with macerated core materials that had been deseeded and destemmed. The mixture was then drum-dried and passed through a 100-mesh screen. The powder was used as a thickener in apple pies. The harsh drying conditions resulted in the loss of most of the aroma from the peels and a brown appearance. The pies made with the apple peel powder did not have higher taste ratings, probably due to the undesirable brown color of the powder.
The need thus remains to find a valuable use of the millions of pounds of waste peels generated from applesauce and canned apple processing each year in this country.